1. Field of the invention
The present invention relates to an apparatus for preparing a preform with a high volume fraction of SiC particles. More particularly, the present invention relates to an apparatus for preparing a preform which is so superior in thermal conductivity and in coefficient of thermal expansion that it can be used as a material for a metal matrix composite useful in electronic packaging and space-air structures. Also, the present invention is concerned with a process for preparing such a preform using the apparatus.
2. Description of the Prior Art
Recently, attention has been paid to metal matrix composites because they are found to be useful as materials not only for electronic packaging, but for space-air structures such as artificial satellites. In a metal matrix composite, the low coefficient of thermal expansion of a ceramic which serves as a reinforcement, restrains the metal matrix from thermally expanding. In addition, preferable coefficients of thermal expansion of a metal matrix composite can be attained by controlling the mole fraction of the reinforcement in the composite. By virtue of these advantages in thermal expansion, metal matrix composites are suitable for use in electronic packaging and space-air structures in which a thermal dimension change is strictly controlled. The reason why the metal matrix composites are of particular interest, also resides in the metal matrix. Metal matrixes have high thermal conductivity, excellent mechanical properties and good processability, which all meet the requirement for the materials for electronic packaging and space-air structures.
In a conventional process for preparing a fiber-reinforced composite, after a slurry of a reinforcement and a binder is mechanically stirred, the medium used is extracted under a vacuum by use of a vacuum assisted extraction method. When a particle-reinforced composite is prepared by the vacuum assisted extraction method, the reinforcement is found to have an average volume fraction of as low as 50%. It is known, however, in order to be used as materials for electronic packaging, metal matrix composites must comprise a reinforcement at a volume fraction of at least 65%.
Noticeable methods for preparing preforms with a high volume fraction of reinforcements are disclosed. For example, WO 96/41030 discloses a preparation method of a preform, which takes a calcining step at 1,700.degree. C. The formation of cuprous oxide which is induced from copper powder under an oxygen or nitrogen atmosphere, is utilized to prepare a preform in U.S. Pat. No. 5,374,391. The method disclosed in U.S. Pat. No. 5,620,511 comprises dispersing silicon micro-particles and carbon fibers in an aluminum alkoxide solution and extracting the solvent under a vacuum. These conventional methods, however, suffer a disadvantage in that they are economically unfavorable because gas atmospheres, high temperatures and expensive large-sized apparatus are needed.